Freshwater ecosystems have been critical to sustaining life and establishing civilizations throughout history, as evidenced by many human settlements worldwide being concentrated near freshwater ecosystems and with over half of the world's population living within 20 kilometers of a permanent river. Unfortunately, as global population has grown, increased agricultural and industrial production combined with poor sanitation practices has led to a widespread increase in water pollution with most freshwater lakes becoming contaminated to some extent by chemical and biological contaminants or pollutants such as Escherichia coli (E. coli) and dissolved nutrients in the form of nitrogen and phosphates. Such contamination has decreased the potability of the water and the ability of fish and other wildlife to survive in these freshwater lakes.
More specifically, the pollution and contamination of freshwater lakes and corresponding reduction in water quality has occurred due, at least in part, from soil erosion, nutrient mismanagement, and pesticide mismanagement. Soil erosion reduces water quality as contaminants and debris present in the soil are carried with surface water that runs off into creeks, streams, rivers and lakes. The contaminated soil then releases its nutrient load, leaching pollutants into the water and promoting growth of autotrophic and heterotrophic microorganisms, including various algae and bacteria such as E. coli. Nutrients also enter creeks, streams, rivers and lakes through runoff, such as storm water from rain or melting snow, which flows from roads, rooftops, farms, and lawns picking up contaminants such as wastewater, fertilizers, lawn treatment chemicals, pesticides, and household chemicals along the way. Such polluted runoff contaminates and degrades the quality of water in creeks, streams, rivers, and lakes, and the polluted runoff can kill or damage plants, fish, and wildlife.
Excess nutrients, such as nitrogen and phosphorous, in raised concentrations increase algae productivity, especially filamentous green algae, and may contribute to out-of-control algae blooms in freshwater lakes. And, excess nitrogen and phosphorous can cause eutrophication, which is the process of increasing organic enrichment or biological productivity leading to increased algae and aquatic weed growth, oxygen shortages, and formation of carcinogens during water chlorination. The eutrophication of natural waters, caused by an increase in dissolved nutrients, is one of the most significant causes of declining water quality. Although eutrophication is a natural process of aging of lakes and water bodies, human activities can greatly accelerate eutrophication by accelerating the rate at which nutrients and organic substances enter aquatic ecosystems from their surroundings. This has occurred at Lake Victoria, the second largest lake in the world and an important water source shared by Kenya, Uganda, and Tanzania, where a surface algal mass is frequent due to increased pollution from humans and industrial waste containing phosphates and nitrates.
Similarly, in Lake Erie of the Great Lakes, phosphorus was shown to be a major nutrient contributing to and controlling phytoplankton growth. In Lake Erie, hypoxia has been directly linked to elevated in-lake total phosphorus concentrations and excessive external total phosphorus loadings. For many years, detergents having phosphates flowed into Lake Erie. Following a ban being placed on phosphates in detergents, total yearly concentrations of phosphorus and dissolved oxygen depletion rates declined significantly. As a result, algal biomass reductions were observed, especially in nuisance and eutrophic species of algae. Prior to the ban, diatom populations tended to dominate the algae species favored by nutrient rich conditions, cyanobacteria were in abundance, as well as the green algae Cladophora and the red algae, Bangia. 
Excess nutrients have also been responsible for the Chesapeake Bay having massive numbers of algal blooms each spring due to fertilizer runoff from local farms and lawns. Then, as the algal blooms die off, resulting decomposition depletes life-supporting oxygen in the water and causes dead zones in the bay. According to some, such harmful algal blooms are excessive accumulations of microscopic photosynthesizing organisms (phytoplankton) that produce biotoxins or that otherwise adversely affect humans, animals, and ecosystems. Most harmful algal blooms are cyanobacteria blooms, but others are nonbacterial blooms from algae like Cladophora, which is known to harbor E. coli populations. The presence of algal masses is, therefore, often associated with elevated E. coli levels.
E. coli are heterotrophic bacteria classified as coliform. In addition to algal blooms and other organic matter, catalysts for E. coli growth include swelling rainfall and other atypical events. The presence of E. coli is also a widely used indicator of contamination originating from domestic sewage. Although for the most part E. coli is not pathogenic, its presence in surface water, especially at elevated levels, can indicate fecal contamination and the likelihood that pathogens such as Salmonella, Streptococci, Cryptosporidium, Giardia, and Enterovirus could be present.
Scientists and engineers have attempted to remove dissolved nutrients and improve the water quality of the Chesapeake Bay and other large bodies of water through the controlled use of algae in devices commonly referred to as Algal Turf Scrubbers (“ATS”). An algal turf is a community of organisms dominated by aggregations of unicellular to branched filamentous algae and cyanobacteria (blue-green algae). Unlike the uncontrolled overgrowth of algae in bodies of water described above, algal growth in Algal Turf Scrubber systems is controlled and beneficial rather than harmful to the water quality. Algal Turf Scrubber systems work with fresh water, brackish water, and salt water, and work in a variety of waste and industrial settings such as water quality treatment plants, farm canals, rivers, and the inside of industrial smoke stacks.
Algal Turf Scrubber systems typically include a series of filtration troughs with thin screens that catch filamentous algae. Solar powered pumps add water to the open troughs from a river or other flowing body of water. The water flows through the open troughs, being filtered along the way, and then trickles back into the flowing body of water or into a stagnant body of water, such as a bay. To keep the Algal Turf Scrubber systems running smoothly and to keep fresh algae in the systems, algae are harvested every five (5) to fifteen (15) days. The harvested algae can then be converted into biofuels such as biodiesel, gasohol, methane, and butanol.
Unfortunately, Algal Turf Scrubber systems are expensive to construct and operate. Algal Turf Systems also comprise permanent installations that require massive areas on land and on water. The average dimensions of a current land-based Algal Turf Scrubber system are 50 meters by 1,800 meters, the length of an average airport runway. To clean the Chesapeake Bay, it has been estimated that a combined 10,000 acres of land-based and floating Algal Turf Scrubber systems would be needed. Thus, the costs of construction and operation and the areas required for Algal Turf Scrubber systems render them impractical for use in reducing the levels of dissolved nutrients in smaller bodies of water. In addition, Algal Turf Scrubber systems do not attempt to directly lower the levels of E. coli bacteria and pathogens such as Salmonella, Streptococci, Cryptosporidium, Giardia, and Enterovirus.
There is, therefore, a need in the industry for an apparatus and method for reducing the levels of dissolved nutrients, reducing the levels of E. coli bacteria and pathogens, improving water quality, and producing potable water from freshwater creeks, streams, rivers and lakes using little land or sea area, and that resolves the difficulties, shortcomings, and problems associated with using Algal Turf Scrubber systems or other technologies with smaller bodies of water.